1. Field of the Invention
The present invention relates to a field-emitter used in a scanning electron microscope or a cathode ray tube, and to a method of producing same.
Increasing research is being made, into micro field-emitters formed on a silicon or glass substrate by utilizing the technology used for manufacturing integrated circuits. The application of the micro-field emitter extends to vacuum tube integrated circuits including an array of vacuum triodes, each composed of a cathode, control electrode and anode, as well as a flat display panel in which cathodes are arranged in a plane and a fluorescent element faces the plane. New advances, therefore, can be expected in this field, and the present invention deals with such a field emitter and a method of producing same.
2. Description of the Related Art
Field-emitters and methods of producing same are known as Gray's method from U.S. Pat. No. 4,307,507 issued on Dec. 29, 1981, and from S.M. Zimmerman, D.B. Colavith and W.T. Babie; Development Progress Toward The Fabrication of Vacuum Microelectronic Devices Using Conventional Semiconductor Processing (Proceedings of IEDM 90, pp. 163-166 (1990)).
The field-emitter cathode and method of manufacturing same developed by Gray et al., are first elucidated. This method is based on the technique whereby one or more very small holes are formed in an etching mask deposited on a silicon single crystal substrate, and the substrate then etched with an anisotropic etching which assures different etching rates according to differences in the crystal orientation, to thereby obtain etched holes having a sharpened bottom tip, with a high reproducibility. For example, when a (100) substrate is etched with an aqueous solution of potassium hydroxide, etched holes in the form of quadrangular pyramid are formed, and thereafter, a cathode material is deposited on the silicon single crystal substrate having the above-described etched holes, to form a thin film thereon. In this case, the film of cathode material may be formed after forming a protective layer on the silicon single crystal substrate. Finally, the cathode is produced by removing, by an appropriate etching, the silicon single crystal substrate utilized as a mold. This method gives quadrangular pyramid-shaped cathodes.
Further, a method of manufacturing microtriodes by S.M. Zimmerman et al is elucidated; FIG. 1 shows the section of an element in the respective stages of manufacture thereof.
As shown in FIG. 1A, a single crystal silicon substrate 23 is oxidized to form an silicon oxide layer 19, and then a silicon nitride layer 20 and polysilicon layer 21 forming a gate electrode are successively deposited.
As shown in FIG. 1B, an opening 22 approximately 2 .mu.m.times.2 .mu.m square is formed, and the silicon nitride layer 20 and silicon oxide layer 19 are etched through the opening 22.
As shown in FIG. 1C, a silicon oxide layer 27 is deposited over the whole surface of the substrate, by a low pressure chemical vapor deposition method (LPCVD method), whereby an inversed cone is formed at the opening in the silicon oxide layer, and subsequently, a polysilicon layer 24 is formed on the whole surface of the substrate by the LPCVD method, as shown in FIG. 1D. In this case, a cathode 26 in the form of the inversed cone is formed at the inversed cone-shaped mold in the silicon oxide layer. Furthermore, as shown in FIG. 1E, an opening 25 is formed, in the vicinity of the cathode 26 made of poly-silicon, in the poly-silicon layer. Finally, a microtriode is produced with a space formed by etching the silicon oxide layer deposited in the initially formed opening 22 through the opening 25.
Nevertheless, several problems arise in the above-described prior arts. Namely, the method of Gray et al., provides a high reproducibility in the shape of the cathode, since the mold is formed by anisotropically etching silicon single crystal, but difficulties remain with the sharpening of the tip of the cathode, with finely fabricating the element, and with forming the control electrode close to the cathode. Furthermore, the edge angle of the cathode tip obtained by this method is determined by the angle of the crystallographic surface obtained by the etching, and this makes it difficult to sharpen the angle of the cathode tip, and thus it becomes impossible to reduce the voltage of the electron emission.
In the method of manufacturing microtriodes proposed by S.M. Zimmerman et al., a mold formed at the opening 22 in the silicon substrate 23, on which the silicon oxide layer 27 is deposited by the LPCVD method, changes the shape and size of the opening 22, depending on the conditions for forming the silicon oxide layer 27, and the thickness of the layer, causing a lower reproducibility of the shape formed. As a result, a high reproducibility of the radius of curvature cannot be obtained for the tip of the produced cathode 26. Moreover, it is difficult to control the position of the cathode tip, due to the change in the shape of the mold. Also, the spacing between the single crystal cathode 26 and substrate 23 for the anode electrode, as well as the mutual relationship between the cathode 26 and polysilicon layer 21, cannot be controlled, and accordingly, the voltage of the electron emission and the electron travelling time changes from element to element. Further, a problem arises with the stability of the electric properties. Namely, the cathode produced by this method has an increased resistivity due to the reduced angle of inclination in the main body, resulting in a destruction of the cathode itself by the Joule's heat.
Therefore, the object of the present invention is to provide a field-emitter ensuring stable electrical properties and a lower electron emission voltage by producing a cathode including a projection having a reduced inclination angle of the tip thereof, and by controlling the positional relationship between the cathode and anode and/or gate, and to provide a method of manufacturing an emitter having the same properties, with a high reproducibility.